Many types of inkjet printing systems include one or more printheads that have arrays of drop ejectors that are controlled to eject drops of ink of particular sizes, colors and densities in particular locations on the print media in order to print the desired image. Each drop ejector includes a nozzle and a drop forming element, such as a bubble-nucleating heater. In some types of printing systems, the array of drop ejectors extends across the width of the page, and the image can be printed one line at a time. However, the cost of a printhead that includes a page-width array of drop ejectors is too high for some types of printing applications, so a carriage printing architecture is often used.
In an inkjet carriage printing system such as a desktop printer, or a large area plotter, the printhead or printheads are mounted on a carriage that is moved past the recording medium in a carriage scan direction as the drop ejectors are actuated to make a swath of dots. At the end of the swath, the carriage is stopped, printing is temporarily halted and the recording medium is advanced. Then another swath is printed, so that the image is formed swath by swath. In a carriage printer, the drop ejector arrays are typically disposed along an array direction that is substantially parallel to the media advance direction, and substantially perpendicular to the carriage scan direction. The length of the drop ejector array determines the maximum swath height that can be used to print an image.
It is desirable to arrange the different drop ejector arrays with relatively small spacing that is on the order of 2 millimeters or less so that the printhead drop ejector die can be compact and low cost. For carriage printers where the ink tanks are mounted on the carriage, it is desirable to make the ink tanks of high enough capacity so that several hundred pages can be printed before changing tanks. Typical ink tank widths are on the order of 10 millimeters. For a carriage printer having four drop ejector arrays and four corresponding ink tanks, the distance between the outermost nozzle arrays is typically around 6 millimeters, while the distance between the outermost ink tanks is typically around 30 millimeters. For carriage printers having more than four drop ejector arrays and corresponding ink tanks, the difference in distances is even larger. Ink distribution lines are provided, typically in a manifold in the printhead, to route the ink from the ink tanks to the drop ejector arrays. Long ink distribution lines can be disadvantageous in that they provide larger regions where air can become trapped in the printhead.
Faster printing throughput can be achieved by printing at a faster carriage speed. However, the distance d required to accelerate from a stopped position to a constant velocity vc is given by d=vc2/2a, where a is the acceleration. Therefore, as the carriage velocity is increased, it is desirable to increase the acceleration so that the width of the acceleration region doesn't increase to unacceptable levels, requiring that the printer be significantly wider than the print media. Such acceleration can cause pressure increases and decreases in the ink distribution lines as the ink sloshes back and forth. In order to further increase printing throughput, some printers print during acceleration and/or deceleration. However, acceleration and deceleration of the carriage can cause ink pressure changes during printing that can result in image quality degradation under certain circumstances, particularly for large magnitudes of acceleration or deceleration.
What is needed is a configuration of ink distribution lines that is less susceptible to large amounts of air becoming trapped, and also less susceptible to pressure surges due to acceleration and deceleration of the carriage.